Optional modulators are solid state micro devices, which are widely used for microdisplay projection and other optical signal processing systems. Optional modulators can control or modulate an incident beam of light in a defined spatial pattern. The defined spatial pattern is correlated to a series of electrical inputs of image to the devices, through which the incident light beam can be modulated in intensity, phase, polarization or direction.
Two of the most commonly used classes of optical and particularly, spatial light modulators employ microelectromechanical system (MEMS) devices in a two dimensional array configured to provide two-dimensional modulation of incident light: Digital Micromirror Device (DMD) from Texas Instruments and the Grating Light Valve (GLV) device from Silicon Light Machines.
The appeal of the DMD has been evidenced in the widespread adoption, given its high optical efficiency, large etendue, wide bandwidth, high modulation speed and digitalized control algorithm for time sequential color combination and management. Despite its success in projection display applications, however, the DMD has been recognized with certain shortcomings, such as high power consumption per pixel, particularly for high resolution microdisplay projection applications in cellphone and handheld devices.
The GLV array devices based in fine reflective metal grids or elements are also recognized with significant appeal in etendue, analog grey-scaling, optical efficiency, modulation speed and particularly, power consumption per pixel. In a either linear or 2 dimensional configuration, a GLV array for modulating incident beams of light, the modulator comprising a plurality of grating elements, each of which includes a light reflective planar surface. Those grating elements are arranged parallel to each other with their light reflective surfaces parallel to each other. The modulator includes electrical-mechanical means for supporting the elements in relation to one another and means for moving the elements relative to one another so that elements move between a first configuration wherein the modulator acts to reflect the incident beam of light as a plane mirror, and a second configuration wherein the modulator diffracts the incident beam of light as it is reflected therefrom. In operation, the light reflective surfaces of the elements remain parallel to each other in both the first and the second configurations and the perpendicular spacing between the reflective surfaces of adjacent elements is equal to m/4 times the wavelength of the incident rays of light, wherein m is an even whole number or zero when the elements are in the first configuration and m is an odd number when the beam elements are in the second configuration.
The core idea of such a GLV modulator includes a reflective deformable grating light modulator, with a grating amplitude that can be controlled electronically, consisting of a reflective substrate with a deformable grating suspended above it. In its undeformed state, with no voltage applied between the elements of the grating and the substrate, the grating amplitude is one half of the wavelength of the incoming light. Since the round-trip path difference between the light reflected from the top and bottom of the grating is one wavelength, no diffraction occurs. When a voltage is applied between the grating elements and the substrate, the electrostatic force pulls the elements down to cause the grating amplitude to become one quarter of the wavelength so that reflections from the elements and the substrate add destructively, causing the light to be diffracted. If the detection system for the reflected light has a numerical aperture which accepts only the zero order beam, a mechanical motion of only one quarter of a wavelength is sufficient to modulate the reflected light with high contrast.
However, the wavelength dependency under a control algorithm with discrete states of light modulation and incident angle sensitivity due to diffraction are evident on the GLV devices disclosed in the prior art. Particularly for microdisplay projection applications, digitalized spatial modulation is desired for modulating illumination of wide incident angle over visible spectrum and in particular, in association with time sequential or spatial mosaic pattern color management schemes.